Power steering means



3,166,143 I POWER-STEERING MEANS Edwin Gonter, Jr., and Robert A.Elliott, South Bend, Ind., assignors to The Bendix Corporation, Southliend, Ind., a corporation of, Delaware Filed Dec. 17, 1962, Ser. No.245,131 8 Claims. (Cl. 18tl79.1)

This invention pertains-to a power steering system and more particularlyto a power steering unit in which a hydro-mechanical power steeringsystem is controlled by an alternating current electric steering controlsystem including variable diflerential transformers and a phasesensitive demodulator circuit.

As stated in U.S. Patent No 3,007,655 assigned to the common assignee,the need for steerable nose wheels on having electrical control meansarranged to be fail-safe in operation.

It is a further object to provide simple durable electrical steeringcontrol means which are extremely lightweight and which require verylittle space.

A still further object 'is to provide in the event of a double failure asteerable nose wheel which is controlled through its inherent casteringaction.

I United 2 States. Patent Other objects and advantages will appear tothose skilled in the art from the accompanying description of the singlefigure which shows a casterable and steerable wheel in combination withsuitable operated hydraulic motor means for controlling the steeredposition of said wheel and electrical actuating means for saidhydraulically actuated'power means. 7

Referring now to the-drawing, a steerable wheel 10 is attached to arotatableshaft 12 by means of an otfset strut 14. Fastened to shaft 12is a link 16 having slots 18 receiving a pair of pins 20 which areattached'toa pair of axially movable shafts Hand 24. Shafts 22 and 24form part of the hydraulic motor system including a to shaft 24 andpositioned within a cylinder 32. A conduit 34 provides communicationbetween the right side of piston 26 and the left side of piston whereasa piston 26 drivably attached to shaft 22 and positioned t withina-cylinder28 and'ia piston 30 drivably connected conduit 36providescommunication between-the left side 1' steering system. If onewere to visualize the removal of cylinder 32 and the conduits 34 and 36as well as the appurtenances, one would readily see such a singleactuator system. I

High pressure servofluid is supplied to the hydraulic motors from asource (not shown) through a solenoid actuated valve 38, a conduit'40,and a check'valve 42 to a control valve outlined as at 44. The controlvalve contains a valve spool 46 having lands 48, 50 and 52 and pistons54 and 56 at each end. A pair of conduits 58 and 6tl providecommunication between the control or servo valve'44, as it may betermed, and opposite ends 3,166,143 Patented Jan. 19., 1965 "ice of thecylinder 28. As shown, the spool valve is in a neutral position blockingflow to the cylinders. Movenient of the spool valve 46 to the rightcommunicates high pressure servo fluid line 40 with conduit 58 to applyfluid pressure on the left side of piston 26 and the right sideof-piston 30. At the same time communication is established betweenconduit 60 and a servo fluid return line 62 to relieve the right andleft sides of cylinders 28 and 32, respectively. Thus, the Wheel 10 willrotate clockwise to steer the associated vehicle (not shown) to theright. Although the wheel arrangement is shown with an aircraftapplication, it is to be understood that the type of actuation isuniversal and could be connected in automobile steering linkages. It isalso to be understood that movement of spool 46 to the left would giveopposite steering for any associated vehicle.

- In order to provide unid-irectionalflow restriction and casterablequalities to wheel'lll, check valves 64 and 66 and orifices 76 and 73are provided in lines 58 and 66, respectively, and lines 60 and 58 arecommunicated to chambers 68 a'nd7il by conduits 72 and 74, respectively.In Patent No. 3,007,655 mentioned there was employed an additionalcontrol valve which is eliminated in our invention by making the spoolvalve responsive to cylinder pressure as above described/ This in turnprovides our'steering system with shimmy damping in both power and nonpower conditions of operation. In addition, a

pair of small bleed orifices 76 and 78 are employed in" check valves 64and 66, respectively, to assist in inhibiting or damping shimmy forceswhich might be transmitted to the actuator pistons 26 and 30 from thewheel 10.

Suppose, for instance, a shimmy oscillation is acting on piston 26 whichfirst causes piston 26 to move to the right.- Fluid is forced out ofcylinder 28 and kinetic energy is transformed to heat by orifice 78 todissipate energy. As pressure builds up in conduit 66 it will act onpiston 54 to cause' the control "valve spool 46 to open conduit 60 tothe system return conduit 62. If, for some reason, return pressure inconduit 62 is higher than inlet pressure, a pressure responsiveunidirectionalflow valve 80 would open return to inlet. 'In case fluidsupply is blocked, this would allow fluid to flow back to the cylinder28 opposite the side from which it came to prevent cavitav tion incylinder 28. In the'event the solenoid actuated valve 38 is open, inletfluid pressure will be supplied to prevent cavitation and it may beassisted by return flow when, as above, return pressure is higher thaninlet pressure. 1

We also employ a compensator valve 82 in the returnsystem,whichinconjunction with check valve 42 and valve 80 operates tomaintain a certain fluid pressure level in the system'be'cause oftemperature changes in the servo In addition to the above means forcontrolling valve spool 46, the valve 44 is controlled throughelectrical means effective to vary the fluid pressure operating againstthe ends of the spool by way of chambers 84 and 86 at each end ofthe'valve spool. As seen, servo pressureis always communicated to achamber90 surrounding land 56 thence to a passage 92 which passage terminatesin restricted orifices 94 and 96. From'the flow restrictors 94' and 96,the fluid or servo pressure is directed through passages 98 and 100to'chambers 84 and 86, respectively.

Bleed passages 102 and 104 are respectively attachedto passages as andtill), which bleed passages end in opposed ports to a chamber-166containing a flapper valve 168 controlled by windings and 112. The valve103 and windings 11d and 112 form a torque motor 114 for spool 46 fromits neutral position shown.

' therebetween.

#7; a) i controlling theamount of iluid which will be exhausted fromchamber-106 byway of passage 116 leading to the return line 62. a I

Inasmuch as the fluid pressure circuits for chambers 84 and'86 areessentially similar, a stream of highpressure fluid is directed againsteach side of flapper valve 1%; and, I as longas it, valve 168, maintainsa neutral position, as

shown, there will be no unbalanced force tending to move Should,however, fiapper valveliiS be moved to a position closer to the outletof either of conduits 1132 or 1%, an unbalanced force will be developeddue to blocking of flow from the.

conduit so approached by valve 108 to raise the pressure in eitherchamber 84 ,or 86 to cause spool 46 to move to relieve such pressureunbalance. In addition, as valve 108 blocks one passage it opens theother further to decrease resistance to spool movement requested.

As maybe readily seenby those skilled in the art, the movement of thespool 46 is such as to set up a flow restriction between conduits 58 and6t) and the return line 62 to resist shimmy effect on spool 46;-i.e., asthe spool 46 is moved by shimmy forces, fluid from one ofthe chambers 63or 65 will be displaced through a restricted passage formed by lands 48and 52 and the walls of return chambers 67 and 69,,which restrictionactsto dissipateenergy, as aforementioned. The response of spool 46 is alsocontrolled by nozzles 117 and 119, which nozzles control fluid flow toreturn 116 from chambers 84 and 86, respectively.

As for the electrical system controlling the signals to windings 110 and112, we have utilized an alternating curj rent (A..C.) system withalternating current forming a power source to conductors 118 and 120.Generally speaking, our alternating current system includes an inputsensor, a phase sensitive demodulator circuit and an output sensor. 7 1

More particularly, we propose to connect an operator controlled steeringmember, rudder pedals, steering wheel, etc., to a variable diiferentialtransducer 122 herein-after referred to as a command transducer having adual sec-I ondary winding with a single primary winding. This connectionis preferably by way of'a mechanical link 124'between the aforementionedsteering mechanism and the movable core .126 The core is arranged toinduce voltage in a dual secondary element having .windings 128 and 130such that the output voltage from the primary to the secondaries isfirst in phase then out-of-phase and with respective high points in eachphase and a null condition The command transducer is in seriesconnection with a feedback transducer 132 having a mechanical link 134with the nose wheel actuator, as'shown. The primary winding 136' isconnected byan appropriate lead" to the power source and to a primarywinding 138 of the command transducer which is then connected to thepower .source by another lead to complete the series arrangement. Y Thedual secondary windings 126 and 128are in series with similar dualsecondary windings 140 and 142,011. the

incorporates an in-phase secondary 148 and an out ofphase secondary 146.Current limiting resistors 150, 152, 154 and 156 reduce the voltage fromthe secondaries 146 and 148. Each of the two secondaries 146 and148 areindependentlyconnected to a demodulator or gate groups of detectorrectifying diodes 158 and 160 having power 172 leading to-thedualsecondary of transducer 132, to I transducer 122 and thence to powertake-off 164 to alternatively connect one of the torque motor windingsto 7 one orthe other demodulator circuits. 7

In order to smooth or flatten the peaks of half wave action, we providecapacitors 174'and 176 in the common lead across the leads from powertake-oifs 162'and 166.

In operation the operator moves his steering control 124 V v to move thecore 125 to a position such that the signal on the other side of thenull position. .At the same time i the core of transducer 132 is actingin accordance with q the azimuth position of wheel and the voltage fromtransducer 132 is bucked against that of transducer 122 take-offs 162,164 and 166. Thus, we have provided a full wave action circuit with eachgate group 158and 160 having half wave action. From power take-off 162we provide a lead to winding 110 and from power take-01f 166 we providealead to winding 112, both of the torque motor 114. The circuit to thewindings 11d and 112 of torque motor 114 is completed by leads 168 and170,"

respectively, commonly connected to another conductor such that thesignal from transducer 122 is compared in both phase and magnitudewith'the A.C. signal of.trans-- ducer 132. The resultant control signalis supplied-to the phase sensitive demodulator or gate circuits 158 and1619. Here the signals are rectified to provide Bi-Polar? direct currentto the four-wire torque motor 114.. ,The

resultant motion of the torque motor arm or flapper valve 1%, as termedpreviously, corresponds to the phaseand magnitude of the control signal,and, as mentioned, controls the position of spool 46 controlling pistons26 and 313 which control the steering of wheel 19;

The demodulator circuit provides for full wave reotification of thesensors A.C. signal with each circuit 153 or 169 or bridge network, asthey may be termed, contributing one half wave, This circuitry allowsfailure of one diode in any bridge network without failure of controlover wheel 1% The gain would be lowered, but only in one direction ofturn. i

To eliminate any possibility of a hard-over signal upon failure of onetransducer, the transducers, both primaries and secondaries, are inseries which means any such failure results in a loss of power and nocontrol signal can be sent.

Although only one embodiment is shown and described herein, it isrecognized that modifications maybe made without departing from thespirit of the present invention. -We claim: ii I. Y V I 1. In a powersteering system including a steerable Wheel, a motor means inciudingacylinder and a piston in said cylinder e'fiective to dividesaid cylinderinto two chambers, which piston is operably connectedfto steer thewheel, servo valve means controlling the motor means, a actuator forsaid servo valve means comprising a a torque motor; and i electricalmeans for controllingsaid torque motor,

which electrical means-includes a differential command tnansducer, adifferential feedback transducer in series with said command transducerand opera- J tively'connected to said wheel, apower transformer i havingmeans to divide a signal'supplied thereto into separate phases, ademodulator "circuit havingparallel connected groups of detectorrectifying diodes each of which receives a separate phase of said signalfrom said powertransformer toprovide intermittent direct current signalswhich singularlyarid combined wheel, apower transformer having phasedividing secondaries and a demodulating circuit of groups of detectorrectifying diodes each group of which is; I separately connected to oneof said 'phasedividing secondaries such that said groups are phasesensitive r v in operation to provide half waveaction, said groups ofdetector rectifying diodes being connected in parallel andto saidcontrol means with alternating.

in-phase end out-of-phase signals each of which is capable in andofitself to actuate said control means; and a means to supply a steeringrequest to said command transducer to vary the conductivity of saiddemodulator circuit to actuate said control means. In anelectro-hydraulic steering system including an alternating currentsupplied power transformer with dual secondaries receivingv said currentfrom series connected command and feedback differential transducersaccording to phase and directing the in-phase and out-of-phaseportions-to separate parallel connected sensitive gate groups ofdetector rectifying diodes with a means to vary the conductivity of saidgate groups to vary a signal controlling a torque motor, a hydraulicsteering means comprising:

steerable wheel;

motor means including a cylinder divided into two chambers by a pistonand a piston rod connecting said motor means to said steerable wheel;

servo valve controlling said motor means, said servo valve having aninlet port, a return port, and control ports separated by a spool valvehaving pressure responsive pistons on each end of said spool valve;

separate conduit means connecting said chambers of said motor means tosaid-control ports while maintaining separation of said chambers;

check valve means in each of said conduits arranged to permit flow fromsaid servo valve to said chambers and provided with bleed passages torestrict flow from either of said chambers to either of said controlports;

means to connect each of said conduits to opposite ends furthercomprising capacitor means to flatten the peak of -half wave action,which capacitor means is located between said command and'feedbacktransducers and said demodulator circuits.

. Acontrol system comprisingr steerable wheel;

a means to position said steerable wheel including "a pressureresponsive servo valve controlling a passage means for a pressureresponsive device, which. pressure responsive device is connected tosa1d steerable wheel, said servo valve being responsive to wheelposition to control fluid "flow from said pressure responsive device aswell as to said pressure responsive device through said passage means; I

fluid supply system connected to said means positioning said steerablewheel, said fluid supply system including an inlet conduit and a returnconduit con- 'nected through said servo valve with means to'mahi- Vtain'a preselected fluid pressure within said fluid supply system;

valve means controlling a bypassed flow from said inlet to said returnconduits to position said servo valve to open either said inlet or saidreturn conduits to said passage means, said valve means being actuatedthrough a pair of electrical windings; and

n electrical control network for actuating said valve, which electricalcontrol system includes a command a transducer having a primary windingand multiple secondary windings with a conductance varying phaseshifting core operatably interposed, a feedback transducer, having aprimary winding and multiple secondary windings with a conductancevarying phase shifting core operatably interposed, a means connectingsaid command transducer primary Winding and said feedback transducerwinding in series to a power source, a power transformer having aprimary Winding in parallel with said primary windings of said commandand feedback transducers and a pair of secondary windings adapted toseparate a signal supplied to said power transformer primary into itsvarious phases, a pair of phase sensitive demodula tor groups one ofwhich is separately connected to one of said power transformersecondaries while the other demodulator group is connected to the otherpower transformer secondary and means to connect said demodulator groupsin parallel through said secondaries of said'command and feedbacktransducers, which secondariesare in series with said electricalwindings of said valve means whereby a signal from either or both ofsaid demodulator circuits energizes one or both of said electrical windings in said valve to operate said valve to control said meanspositioning said steerable wheel.

. A control system according to claim 5 andfurther comprising a pair ofcapacitors individually in parallel with each of said electricalwindings of said valve means.

. A control system comprising:

steerable wheel;

means to position said steerable wheel including a pressure responsiveservo valve; fluid supply system connected to said means positioningsaid steerable wheel, said fluid supply system including an inletconduit, a return conduit interposed with said servo valve, and a meansto maintain a preselected fluid pressure within said fluid supply anelectrical control network for actuating said valve,

which electrical control network includes a cornni'and transducer havinga primary winding and multiple secondary windings with a conductancevarying phase shifting core operatably interposed, a feedback transducerhaving a primary Winding and multiple secondary windings with aconductance varying, phase shifting core operatably interposed, a, meansconnecting said command transducer primary Winding and said feedbacktransducer winding in seriesto a power source, a powertransformer havinga' primary winding connected to said. power source and a pair ofsecondary windings adapted to separate an in-phase and an out-of-phasesignal supplied'to said power transformer primary winding, a pair ofphase sensitive demodulator groups, one of which is separately connectedto one of said power transformer secondaries strengthening the in-phasesignal with the other demodulator group being connected to theout-of-phase secondary winding and means to complete the electricalcontrol network connecting the demodulator groups in parallel throughsaid command and feedback secondaries, which command and feedbacksecondaries are in series, to a com- ,mon connector and through a pairof capacitors with leads from each of said demodulator groups beingconnected severally to respective windings of said.

valve. r l A control system comprisingz steerable wheel;

means to position said steerable wheel, including a valve means havingan electrical actuator; and

an electrical control network for actuating said valve,

which network includes a command transducer-haw ing a'primary windingand multiple secondarywind- .ings with a conductance varying, phaseshifting core electrically operatably interposed, a feedback transducerhaving a primary Winding and multipie secondary windings 'with aconductance varying, phase shifting core operatably interposed, a meansconnecting said corn 1 mand and feedback transducers in series with apower source, a' means connecting said secondaries in series witheachother, a power transformer having a prirately connected to one oisaid power transformer secondaries strengthening'the iii-phase signalWith the other demodulator group being'connected to the out-of-phasesecondary winding and means to cornplete the electrical control networkconnecting the derriodulator groups in parallel throughrthe'meansconnecting said transducer secondaries to a common conneotorand througha pair I of capacitors to, said groups with leads from each of said'demodulator groups being severally connected to said electrical actuatorof said valve means.

Referencesfiited in the file of this patent UNITED STATES PATENTS. a

Blanchard Nov. 26, Bennett et al. Aug.'25, 1959; Olson Sept. 22, 1959Barr et a1. Sept. 20, 1960,

Criswell et all Nov. 7,

1. IN A POWER STEERING SYSTEM INCLUDING A STEERABLE WHEEL, A MOTOR MEANSINCLUDING A CYLINDER AND A PISTON IN SAID CYLINDER EFFECTIVE TO DIVIDESAID CYLINDER INTO TWO CHAMBERS, WHICH PISTON IS OPERABLY CONNECTED TOSTEER THE WHEEL, SERVO VALVE MEANS CONTROLLING THE MOTOR MEANS, ANACTUATOR FOR SAID SERVO VALVE MEANS COMPRISING: A TORQUE MOTOR; ANDELECTRICAL MEANS FOR CONTROLLING SAID TORQUE MOTOR, WHICH ELECTRICALMEANS INCLUDES A DIFFERENTIAL COMMAND TRANSDUCER, A DIFFERENTIALFEEDBACK TRANSDUCER IN SERIES WITH SAID COMMAND TRANSDUCER ANDOPERATIVELY CONNECTED TO SAID WHEEL, A POWER TRANSFORMER HAVING MEANS TODIVIDE A SIGNAL SUPPLIED THERETO INTO SEPARATE PHASES, A DEMODULATORCIRCUIT HAVING PARALLEL CONNECTED GROUPS OF DETECTOR RECTIFYING DIODESEACH OF WHICH RECEIVES A SEPARATE PHASE OF SAID SIGNAL FROM SAID POWERTRANSFORMER TO PROVIDE INTERMITTENT DIRECT CURRENT SIGNALS WHICHSINGULARLY AND COMBINED CONTROL SAID TORQUE MOTOR.